Process for the preparation of aldehydes by catalytic gas phase hydrogenation of carboxylic acid or their derivatives with the aid of a tin catalyst

ABSTRACT

Process for the preparation of aldehydes by catalytic gas phase hydrogenation of carboxylic acid or their derivatives with the aid of a tin catalyst 
     The invention relates to a process for the preparation of aldehydes by catalytic gas phase hydrogenation of carboxylic acids or carboxylic acid derivatives at elevated temperature, which comprises employing at tin catalyst supplied to an oxidic support material.

The present invention relates to a process for the preparation ofaromatic and aliphatic aldehydes by catalytic gas phase hydrogenation ofaromatic and aliphatic carboxylic acids or their derivatives with theaid of a tin catalyst.

The preparation of aromatic or aliphatic aldehydes by reduction of thecorresponding carboxylic acids with molecular hydrogen over variouscatalysts is known. The oldest technique goes back to U.S. Pat. No.3,935,265, in which alkyl esters of aromatic carboxylic acids arereacted with hydrogen over aluminum oxide at 400° to 600° C. to givearomatic aldehydes. For example, benzaldehyde is obtained frommethylbenzoate with a selectivity of 37% at a conversion of 39%.

It is furthermore known that zirconium dioxide, by itself or doped withoxides of other metals, such as chromium, manganese, iron, zinc, cobalt,bismuth, lead, rhenium or elements of main group III, such as boron,aluminum, gallium, indium or thallium (EP 150961), or together withoxides or elements of the lanthanide group (U.S. Pat. No. 4,328,373), iscapable of hydrogenating carboxylic acids or derivatives thereof to givethe corresponding aldehydes. According to U.S. Pat. No. 4,328,373, aswell as zirconium oxide, oxides of yttrium, cerium, praseodymium,thorium and uranium on aluminum oxide can be employed. EP 573087describes a catalyst which comprises the oxides of aluminum, manganese,zinc and copper and is prepared by coprecipitation of the correspondingsalts.

The use of tin oxides for the reduction of carboxylic acids withhydrogen to give the corresponding aldehydes is described in U.S. Pat.No. 4,950,799 and in EP 539274. According to U.S. Pat. No. 4,950,799, aV₂ O₅ /SnO₂ mixed oxide catalyst, which can be applied to a support,such as, for example, the oxides of aluminum, titanium, iron, manganese,zirconium, chromium, lead or cobalt, was used for reduction ofm-phenoxybenzoic acid. The selectivity, based on the aldehyde, was only44% at a conversion of 54%. EP 539274 describes the hydrogenation ofcarboxylic acids using a bimetallic catalyst of the type Ru-Sn-B/γ-Al₂O₃. Thus, for example, benzoic acid can be converted into benzaldehydewith a selectivity of 76% at a conversion of 76%. In both cases, theyield of aldehyde is in a range which is industrially unacceptable, andfurthermore complicated multi-component systems, the preparation ofwhich also requires expensive starting materials in the case of EP 539274, are employed as the catalyst.

There is thus a need for a process which avoids the disadvantagesmentioned, which operates with a readily accessible and inexpensivecatalyst system and which produces the aldehydes in a high yield andpurity.

This object is achieved by a process for the preparation of aldehydes bycatalytic gas phase hydrogenation of carboxylic acids or carboxylic acidderivatives at elevated temperature, which comprises employing a tincatalyst applied to an oxidic support material.

The catalyst system to be employed according to the invention can beprepared by simple processes from readily accessible materials and givesvery good space/time yields for the hydrogenation of acids. The use of acomplicated multi-component system and the use of expensive startingsubstances, such as zirconium dioxide and rare earth metals, is avoided.

Suitable oxidic support materials are, for example, aluminum oxide,zirconium oxide, iron oxide, titanium oxide or yttrium oxide, aluminumoxide being particularly advantageous for reasons of cost.

The catalyst system which can be employed according to the invention canbe prepared by impregnation or coprecipitation and subsequent drying andcalcining. In the first case, a solution of a suitable tin compound isapplied to the chosen support, which can be in the form of an oxide orhydroxide, by spraying or by soaking. The tin can be present in thecompounds both as Sn(II) and as Sn(IV). Suitable compounds are, forexample, tin halides, tin sulphates, tin oxalates, tin carboxylates, tinalkoxides, tin hydroxides and di-tin and organotin compounds. Theimpregnated supports are then dried at 100° to 150° C., preferably at130° C. and calcined at 400° to 900° C., preferably at 500° to 700° C.The catalysts thus prepared can be further processed to pellets orextrudates by the customary processes.

In the second case, suitable metal salts of the support materials andsuitable tin compounds can be coprecipitated at pH values of 6 to 10.The choice of metal salts depends on the availability of the salts forthe corresponding catalyst. For example, the nitrate is preferred in thecase of aluminum, while the oxynitrate or oxydichloride is suitable inthe case of zirconium. After the precipitation, the hydroxides arefiltered off and washed with a suitable solvent. Drying is carried outat 100° to 150° C., preferably at 130° C., if appropriate by applying avacuum, and calcining is carried out at 400° to 900° C., preferably at500° to 700° C. A suitable time for the calcining is 2 to 10 hours. Thetin catalyst thus prepared is in the form of granules and can beemployed directly in the reaction after comminution to the desiredparticle size.

In many cases, it has proved appropriate to employ the tin in an atomicratio to the support of 0.001/1 to 0.5/1, preferably 0.005/1 to 0.2/1.

Before the reduction of the carboxylic acids, it is advantageous topreform the catalyst at higher temperatures with a suitable reducingagent. The hydrogenation reaction of the carboxylic acids can be carriedout in a continuous or batchwise procedure. It has proved favorable towork at a temperature of 250° to 600° C., in particular 300° to 400° C.,under a pressure of 0.1 to 10 bar, in particular under atmosphericpressure. The hydrogenation can be carried out with molecularhydrogenation, which can also be prepared in situ. It is also possibleto dilute the hydrogen with an inert gas, such as nitrogen or argon. Thecarboxylic component can be fed to an evaporator as a solid, as a meltor as a solution in a suitable solvent, such as benzene, toluene, xyleneor cyclohexane, and can then be fed in the gas phase to the catalyst tobe employed according to the invention. In many cases, it has provedappropriate if the molar ratio of the carboxylic component to hydrogenis 1:1 to 1:500, and the process is preferably carried out with a ratioof 1:5 to 1:50. The feed rate for the carboxylic acids and theirderivatives is expediently 0.01 to 2 mg/ml_(cat) *h (LHSV: liquid hourlyspace velocity), and that of the hydrogen is 100 to 10,000 h⁻¹ (GHSV:gas hourly space velocity).

According to the present invention, aliphatic and aromatic carboxylicacids and derivatives thereof can be hydrogenated to the correspondingaldehydes. Particularly suitable derivatives are, for example, estersand anhydrides.

The process is of great interest for carboxylic compounds of theformulae (I) and (II) ##STR1## in which R¹ is hydrogen, straight-chainor branched C₁ -C₈ -alkyl, straight-chain or branched C₁ -C₈ -alkoxy, R³-substituted phenyl, naphthyl, R³ - substituted phenoxy, R³ -substitutedbenzyl, R³ -substituted benzyloxy, hydroxyl, amino, NH-(C₁ -C₈ -alkyl) ,N-(C₁ -C₈ -alkyl)₂, halogen or COR⁴,

R² is hydrogen, straight-chain or branched C₁ -C₈ -alkyl, straight-chainor branched C₁ -C₈ -alkoxy or R³ -substituted phenyl, or in which R¹ andR² together can form a fused benzene ring, which can be substituted byhydroxyl, amino, methyl, ethyl, methoxy or ethoxy,

R³ can be hydrogen, straight-chain or branched C₁ -C₈ -alkyl,straight-chain or branched C₁ -C₈ -alkoxy, hydroxyl, amino or halogen,

R⁴ is hydroxyl, C₁ -C₄ -alkoxy, chlorine, bromine or the group ##STR2##in which, in the latter case of anhydride formation, R¹ does not assumethe meaning COR⁴,

X¹ is --O--, --N--, --S--, N═CH-- or --CH═CH-- or,

R⁵ is hydrogen or straight-chain or branched C₁ -C₈ -alkyl,

R⁶ is hydrogen, straight-chain or branched C₁ -C₈ -alkyl, R³-substituted phenyl or halogen,

R⁷ is hydrogen, straight-chain or branched C₁ -C₈ -alkyl or R³-substituted phenyl, in which the C₁ -C₈ -alkyl can be substituted byhalogen, methoxy or ethoxy and in which R⁶ and R⁷ furthermore togethercan be dimethylene, tetramethylene or pentamethylene, and

R⁸ is hydroxyl, C₁ -C₄ -alkoxy, chlorine, bromine or the group--O--CO--C(R⁵, R⁶, R⁷).

The process is important, for example, for compounds of the formula(III) ##STR3## in which R¹¹ is hydrogen, straight-chain or branched C₁-C₈ -alkyl, straight-chain or branched C₁ -C₈ -alkoxy, R¹³ -substitutedphenyl, R¹³ -substituted phenoxy, hydroxyl, amino, NH-(C₁ -C₈ -alkyl),N-(C₁ -C₈ -alkyl)₂ or halogen,

R¹³ is hydrogen, straight-chain or branched C₁ -C₈ -alkyl,straight-chain or branched C₁ -C₈ -alkoxy, hydroxyl or halogen,

R¹⁴ is hydroxyl, methoxy, ethoxy or chlorine and

X² is --CH═CH or --N═CH--, preferably --CH═CH--, so that aromaticcarboxylic acids or derivatives thereof which are preferably employedare those of the formula (IV) ##STR4## in which R²¹ is hydrogen,straight-chain or branched C₁ -C₄ -alkyl, straight-chain or branched C₁-C₄ -alkoxy, R²³ -substituted phenyl, R²³ -substituted phenoxy,hydroxyl, amino, methylamino, ethylamino, dimethylamino, diethylamino,fluorine or chlorine,

R²³ is hydrogen, straight-chain or branched C₁ -C₈ -alkyl,straight-chain or branched C₁ -C₄ -alkoxy, hydroxyl, fluorine orchlorine and

R¹⁴ has the abovementioned scope of meaning.

The process also has particular importance for compounds of the formula(V) ##STR5## in which R¹⁵ is hydrogen, methyl or ethyl,

R¹⁶ is hydrogen, straight-chain or branched C₁ -C₈ -alkyl or phenyl,

R¹⁷ is hydrogen, methyl or ethyl, or in which R¹⁶ and R¹⁷ furthermoretogether can be tetramethylene or pentamethylene, and

R¹⁸ is hydroxyl, methoxy, ethoxy or chlorine.

The process has great industrial interest if benzoic acid, chlorobenzoicacid, fluorobenzoic acid, methylbenzoic acid, methoxybenzoic acid,phenoxybenzoic acid, tert-butylbenzoic acid, p-isopropylbenzoic acid,pivalic acid, 6-methoxy-[2]-naphthoic acid or methyl or ethyl estersthereof are employed.

The aldehydes prepared according to the invention are widely used asindustrial intermediates in the preparation of plant protection agents,pharmaceuticals or odiferus substances.

EXAMPLES

Catalyst A:

To prepare a coprecipitated catalyst, 361.0 g of Al₂ O₃.9H₂ O and 12.5 gof SnCl₄ are dissolved in 1.5 l of water, the solution is cooled to 5°C. and the pH of the solution is brought to pH=9 with dilute ammoniasolution. The precipitate is filtered off and washed with water. Dryingis carried out at 130° C. and calcining is carried out at 600° C. Aftercomminution to particle sizes of 10 to 20 mesh, the catalyst ispreformed in a stream of hydrogen at 450° C.

Catalyst B:

To prepare an impregnated catalyst, 25 g of Al₂ O₃ is initiallyintroduced into a flask and a solution of 200 ml of ethanol and 10 g ofSn(O^(t) Bu) 4 is added. After thorough mixing of the sample, thesolvent is cautiously distilled off and the residue is calcined at 600°C. After shaping of the catalyst to a particle size of 10 to 20 mesh,the catalyst is preformed in a stream of hydrogen at 450° C.

Examples 1 and 2

The hydrogenations are carried out in a tubular reactor. The catalystbed volume was 20 ml. The evaporation of the benzoic acid employed iscarried out in an upstream evaporator. The GHSV, LHSV and temperatureare adjusted as shown in Table 1. The reaction mixture is condensed witha condenser and analyzed by gas chromatography.

                  TABLE 1                                                         ______________________________________                                                                     Temp-                                            Exam-                        era-          Selec-                             ple   Catalyst GHSV    LHSV  ture  Conversion                                                                            tivity                             ______________________________________                                        1     A        1250    0.13  380° C.                                                                      69%     95%                                2     B        1250    0.12  350° C.                                                                      94%     92%                                ______________________________________                                    

Examples 3 to 13

The experiments are carried out as in Examples 1 and 2. Instead ofbenzoic acid, other aromatic or aliphatic acids or derivatives thereofare employed. The results are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Example                                                                            Catalyst                                                                           Substrate   GHSV                                                                              LHSV                                                                              Temp.                                                                             Conversion                                                                          Selectivity                           __________________________________________________________________________    3    A    p-chlorobenzoic acid                                                                      1250                                                                              0.12                                                                              380° C.                                                                    99%   69%                                   4    B    p-chlorobenzoic acid                                                                      1250                                                                              0.08                                                                              350° C.                                                                    97%   66%                                   5    B    p-fluorobenzoic acid                                                                      1250                                                                              0.10                                                                              380° C.                                                                    95%   83%                                   6    B    p-methoxybenzoic acid                                                                     1250                                                                              0.08                                                                              380° C.                                                                    96%   58%                                   7    B    6-methoxy-2-naphthoic                                                                     1250                                                                              0.14                                                                              380° C.                                                                    90%   35%                                             acid                                                                8    B    3-phenoxybenzoic acid                                                                     1250                                                                              0.12                                                                              380° C.                                                                    96%   88%                                   9    B    p-isopropylbenzoic acid                                                                   1250                                                                              0.06                                                                              350° C.                                                                    99%   85%                                   10   B    p-methylbenzoic acid                                                                      1250                                                                              0.15                                                                              380° C.                                                                    93%   88%                                   11   B    p-tert-butylbenzoic                                                                       1250                                                                              0.08                                                                              350° C.                                                                    96%   91%                                             acid                                                                12   B    methyl benzoate                                                                           1250                                                                              0.07                                                                              350° C.                                                                    91%   87%                                   13   B    pivalic acid                                                                              1250                                                                              0.10                                                                              380° C.                                                                    93%   82%                                   __________________________________________________________________________

We claim:
 1. A process for the preparation of an aldehyde by catalyticgas phase hydrogenation of a carboxylic acid or carboxylic acidderivative, the derivative selected from the group consisting of esters,acid anhydrides, acid chlorides and acid bromides, at elevatedtemperature, which comprises the steps of:applying a tin catalyst to anoxidic support material to form a catalyst, and hydrogenating thecarboxylic acid or carboxylic acid derivative in the presence of thecatalyst.
 2. The process as claimed in claim 1, wherein the tin isemployed in an atomic ratio to the oxidic support of 0.001:1 to 0.5:1.3. The process as claimed in claim 1, wherein aluminum oxide, zirconiumoxide, iron oxide, titanium oxide or yttrium oxide is used as the oxidicsupport.
 4. The process as claimed in claim 1, wherein the hydrogenationis carried out at a temperature of 250° to 600° C.
 5. The process asclaimed in claim 1, wherein the hydrogenation is carried out under apressure of 0.1 to 10 bar.
 6. The process as claimed in claim 1, whereinthe molar ratio of carboxylic component to hydrogen is 1:1 to 1:500. 7.The process as claimed in claim 1,wherein the feed rate for thecarboxylic component is 0.01 to 2 g/ml_(cat) ×h and the feed rate of thehydrogen is 100 to 10,000 h⁻¹.
 8. Process as claimed in claim 1,whereinthe carboxylic acid or carboxylic acid derivative employed is a compoundof the formula (I) or (II) ##STR6## in which R¹ is hydrogen,straight-chain or branched C₁ -C₈ -alkyl, straight-chain or branched C₁-C₈ -alkoxy, R³ -substituted phenyl, naphthyl, R³ -substituted phenoxy,R³ -substituted benzyl, R³ -substituted benzyloxy, hydroxyl, amino,NH-(C₁ -C₈ -alkyl), N-(C₁ -C₈ -alkyl)₂, halogen or COR⁴, R² is hydrogen,straight-chain or branched C₁ -C₈ -alkyl, straight-chain or branched C₁-C₈ -alkoxy or R³ -substituted phenyl, or in which R¹ and R² togethercan form a fused benzene ring, which can be substituted by hydroxyl,amino, methyl, ethyl, methoxy or ethoxy, R³ can be hydrogen,straight-chain or branched C₁ -C₈ -alkyl, straight-chain or branched C₁-C₈ -alkoxy, hydroxyl, amino or halogen, R⁴ is hydroxyl, C₁ -C₄ -alkoxy,chlorine, bromine or the group ##STR7## in which, in the latter case ofanhydride formation, R¹ does not assume the meaning COR⁴, X¹ is --O--,--N--, --S--, N═CH-- or --CH═CH-- or, R⁵ is hydrogen or straight-chainor branched C₁ -C₈ -alkyl, R⁶ is hydrogen, straight-chain or branched C₁-C₈ -alkyl, R³ -substituted phenyl or halogen, R⁷ is hydrogen,straight-chain or branched C₁ --C₈ -alkyl or R³ -substituted phenyl, inwhich the C₁ -C₈ -alkyl can be substituted by halogen, methoxy or ethoxyand in which R⁶ and R⁷ furthermore together can be dimethylene,tetramethylene or pentamethylene, and R⁸ is hydroxyl, C₁ -C₄ -alkoxy,chlorine, bromine or the group --O--CO--C(R⁵, R⁶, R⁷).
 9. The process asclaimed in claim 1,wherein the aromatic carboxylic acid or derivativethereof employed is a compound of the formula (III) ##STR8## R¹¹ ishydrogen, straight-chain or branched C₁ -C₈ -alkyl, straight-chain orbranched C₁ -C₈ -alkoxy, R¹³ -substituted phenyl, R¹³ -substitutedphenoxy, hydroxyl, amino, NH-(C₁ -C₈ -alkyl), N-(C₁ -C₈ -alkyl)₂ orhalogen, R¹³ is hydrogen, straight-chain or branched C₁ -C₈ -alkyl,straight-chain or branched C₁ -C₈ -alkoxy, hydroxyl or halogen, R¹⁴ ishydroxyl, methoxy, ethoxy or chlorine and X² is --CH═CH or --N═CH--,preferably --CH═CH--, so that the aromatic carboxylic acid or derivativethereof employed is preferably one of the formula (IV) ##STR9## in whichR²¹ is hydrogen, straight-chain or branched C₁ -C₄ -alkyl,straight-chain or branched C₁ -C₄ -alkoxy, R²³ -substituted phenyl, R²³-substituted phenoxy, hydroxyl, amino, methylamino, ethylamino,dimethylamino, diethylamino, fluorine or chlorine, R²³ is hydrogen,straight-chain or branched C₁ -C₈ -alkyl, straight-chain or branched C₁-C₄ -alkoxy, hydroxyl, fluorine or chlorine and R¹⁴ is defined above.10. The process as claimed in claim 1,wherein the aliphatic carboxylicacid or derivative thereof employed is one of the formula ##STR10## inwhich R¹⁵ is hydrogen, methyl or ethyl, R¹⁶ is hydrogen, straight-chainor branched C₁ -C₈ -alkyl or phenyl, R¹⁷ is hydrogen, methyl or ethyl,or in which R¹⁶ and R¹⁷ furthermore together can be tetramethylene orpentamethylene, and R¹⁸ is hydroxyl, methoxy, ethoxy or chlorine. 11.The process as claimed in claim 1,wherein benzoic acid, chlorobenzoicacid, fluorobenzoic acid, methylbenzoic acid, methoxybenzoic acid,phenoxybenzoic acid, tert-butylbenzoic acid, p-isopropylbenzoic acid,pivalic acid, 6-methoxy-[2]-naphthoic acid or the methyl or ethyl esterthereof is employed.
 12. The process as claimed in claim 1, wherein thetin is employed in an atomic ratio to the oxidic support of 0.005:1 to0.2:1.
 13. The process as claimed in claim 1, wherein the hydrogenationis carried out at a temperature of from 300° to 400° C.
 14. The processas claimed in claim 1, wherein the hydrogenation is carried out under apressure of 1 bar.
 15. The process as claimed in claim 1, wherein themolar ratio of carboxylic component to hydrogen is 1:5 to 1:50.
 16. Theprocess as claimed in claim 1, wherein the oxidic support material isaluminum oxide.
 17. The process as claimed in claim 1, wherein the tincatalyst is applied to the oxidic support material by impregnation ofthe support material with a solution of a tin compound and then drying,or by coprecipitation of a solution of a tin compound and a metal saltof the support material at pH values of 6 to 10 and then filtering anddrying.
 18. The process as claimed in claim 17, wherein the tin compoundis selected from the group consisting of tin halides, tin sulphates, tinoxalates, tin carboxylates, tin alkoxides and tin hydroxides.
 19. Theprocess as claimed in claim 17, wherein the tin compound is a di-tin ororganotin compound.
 20. The process as claimed in claim 17, wherein themetal salt of the support material is aluminum nitrate, zirconiumoxynitrate, or zirconium oxydichloride.
 21. The process as claimed inclaim 17, wherein the hydrogenation is carried out at a temperature of250° to 600° C. and under a pressure of 0.1 to 10 bar, and wherein thetin catalyst is employed in an atomic ratio to the oxidic support of0.001:1 to 0.5:1.
 22. The process as claimed in claim 1, wherein tin isthe only metal catalyst used in the hydrogenation.